lipids

• Lipids


  Diverse group of chemicals that are fats and oily substances
• Lipids


  • Hydrophobic
  • Insoluble in water
  • Soluble in organic solvents such as ether, ethanol, acetone, chloroform, benzene, etc.
• Types of lipids


  • Simple lipids
  • Complex lipids
  • Derived lipids
• Simple lipids


  Esters of fatty acids with alcohols
• Types of simple lipids

  • Fats
  • Waxes
• Fats


  • Esters of fatty acids with glycerol
  • Solid at room temperature
  • Some are liquid at room temperature and are known as oils
  • Physical state depends on the nature of fatty acids
  • Fats are rich in saturated fatty acids
  • Oils are rich in unsaturated fatty acids
• Waxes


  • Esters of higher fatty acids with higher mono hydroxy aliphatic alcohols (e.g. cetyl alcohol)
  • Have very long straight chain of 60-100 carbon atoms
  • Can take up water without getting dissolved in it
  • Used as bases for the preparation of cosmetics, ointments, polishes, lubricants and candles
  • Found on the surface of plants and insects
• Complex lipids


  Contain some non-lipid substances in addition to fatty acids and alcohol, such as proteins, carbohydrates, phosphate, sulphate, nitrogen etc.
• Types of complex lipids

  • Phospholipids
  • Glycolipids
  • Sulpholipids
  • Lipoproteins
• Phospholipids


  • Made up of fatty acids, an alcohol, phosphoric acid and a nitrogenous base
  • Examples are lecithin, cephalin and sphingomyelin
• Glycolipids


  • Made up of a fatty acid, an alcohol and some carbohydrates
  • Classified into cerebrosides and gangliosides
• Cerebrosides


  Made up of a fatty acid, sphingosine (an amino alcohol) and a carbohydrate (galactose)
• Gangliosides


  Made up of a fatty acid, sphingosine, N-acetyl-neuraminic acid and some hexoses
• Lipoproteins


  • Conjugated proteins or compound lipids made up of lipids (triglycerides, phospholipids, cholesterol and fatty acids) combined with specific proteins
  • Soluble in water because of their protein content
  • The form in which lipids are transported in circulation
• Derived lipids


  • Compounds obtained on hydrolysis of simple and compound lipids, possessing properties of lipids
  • Examples are fatty acids, higher alcohols, sterols, steroids, hydrocarbons etc.
• Steroids


  • Lipids containing a steroid nucleus (core structure) consisting of three cyclohexane rings and one cyclopentane ring
  • Attachment of different groups to the core steroid structure leads to a wide variety of steroid compounds, including cholesterol, bile salts and steroid hormones
• Chemical reactions of lipids

  1. Hydrolysis: Ester bonds of lipids can be hydrolysed by specific enzymes

  2. Saponification: Hydrolysis of triglycerides by alkalis, resulting in the formation of alkali salts of fatty acids (soaps)

  3. Hydrogenation: Double bonds of unsaturated fatty acids can be hydrogenated in the presence of catalysts e.g. nickel

  4. Iodination: Iodine can also reduce the double bonds of unsaturated fatty acids

  5. Oxidation: Unsaturated fatty acids can react with atmospheric oxygen to form fatty acid peroxides, fatty acids epoxides and fatty acid aldehydes